Stripping mechanism for drum dryer doctor blade



G. DOUKAS 3,299,527

S TRIPPING MECHANISM FOR DRUM DRYER DOCTOR BLADE Jan. 24, 1967 Filed Aug. 28, 1963 INVENTOR GEORGE DOUKAS ATTORNEY United States Patent 3,299,527 STRIPPING MECHANISM FOR DRUM DRYER DOCTOR BLADE George Doukas, Beaumont, Tex., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a

corporation of Delaware Filed Aug. 28, 1963, Ser. No. 305,034

6 Claims. (Cl. 34-12) This invention relates to an improvement in drum dryers and more particularly to an improved method of removing solid polymeric material from a drum.

Drum dryers are devices in which materials to be dried are applied continuously in :thin layers to one or more heated revolving drums. These materials are dried as the drum revolves and, finally, are continuously removed from the drum by a scraping device known as a doctor knife. Drum dryers are well known in the art and are Widely used for the preparation of dry material from solutions, slurries, dispersions, or the like. The dried solid material obtained, depending on its physical characteristics, may be removed as flakes, lumps or continuous sheets.

Many important elastomers and other solid polymeric materials are prepared first in solution or latex form and are isolated as solids by drum drying the solution or latex.

In this well known procedure, a thin layer of the solution or latex is coated on the drum and the volatile liquid is riven off thereby forming a coherent coating of polymeric material on the drum. The latter is ordinarily removed by the doctor knife as a sheet which is gathered on a wind-up roll. Unfortunately, however, this procedure results in a great deal of wastage which is caused by tears in the film occurring between the doctor knife and the wind-up roll. Further, this technique requires that the latex or solution contain a sufiiciently high solids content of polymeric material from which to form a selfsupporting sheet.

It has been found that the amount of wastage is greatly reduced by gathering the solid polymeric material in particulate form. This is uniquely accomplished by the subject invention which is particularly pointed out in the appended claims and is illustrated, in its preferred embodiments in the accompanying drawings wherein:

FIG. 1 is a schematic elevational View of a portion of an improved drum dryer according to this invention.

FIG. 2 is a partial sectional view taken along line 22 of FIG. 1 including a sectional view of the air knife and tray which are omitted from FIG. 1 for the sake of clarity.

Referring now to the drawings, the drum dryer shown therein comprises a drum 10 having a doctor knife 11 mounted in association therewith; the details of mounting the doctor knife are omitted for the sake of clarity but are well known to those skilled in the art. The doctor knife 11 has mounted thereover a plate 12 having a plurality of fingers 13 extending therefrom toward the doctoring edge of the doctor knife 11. An air cylinder 14 is provided with a piston 15 which is attached to connecting rod 16 with the latter being attached to the plate 12. A pair of air hoses 17 and 18 are connected from valves at the opposite ends of the air cylinder 14 to a suitable source of alternating air pressure (not shown). Upon the application of air pressure to hose 17, the piston 15, connecting rod 16 and, consequently, plate 12 are moved to the right. Conversely, application of air pressure through hose 13 serves to move the plate 12 to the left. By the alternate application of pressure to the hoses 17 and 18 the fingers 13 are oscillated in movement along the doctoring edge of doctor knife 11. The extremities 19 of the plate 12 are mounted in suitable means (not shown) which provide proper support for the plate in a desired position but enable axial oscillatory movement thereof; such means are readily apparent to one skilled in the art.

Referring specifically to FIG. 2 it can be seen that air knife 20 permits the direction of an air stream at the doctor knife 11 and fingers 13. Preferably, the air stream is uniformly distributed along the entire length of the doctor knife at the point where the stripped polymeric material begins to roll up into particulate noodles or cigars 21. A tray 22 is provided to receive the particulate material 21 and conduct it to a suitable receptacle (not shown).

The fingers 13 are positioned in close proximity to the doctor knife 11 and the rotating drum 1!); the exact degree of separation can be selected by those skilled in the art in order to achieve the most efiective removal of polymeric material from the doctor knife with each stroke of the oscillating fingers.

The shape of the fingers 13 is not critical; representative fingers are cylindrical or conical or truncated conical; other representative fingers are flat, convex, or concave plates having parallel or sloping sides; typical fingers have fiat, pointed, or rounded ends. I

The rate of oscillation depends upon the rate at which the drum It) is rotated, the faster the rotation, the higher the rate of oscillation. The speed at which the fingers 13 oscillate affects the diameter of the stringy noodles 21 formed at each finger. Faster oscillation yields smaller diameter particles. If the particles 21 become entangled in the fingers, those skilled in the art can readily avoid this problem by routine adjustment of the operating conditions and by modification of the finger design.

The process embodiments of this invention will be more clearly understood in reference to the following example of a preferred embodiment thereof wherein parts and percentages are by weight unless otherwise specified.

Example 4% (solids content) solution of an ethylene/propylene/1,4-hexadiene copolymer in te tra chloroethylene is prepared according to the general directions of US. Patent 2,933,480 using a vanadium oxytrichloride/diisobutyl aluminum monochloride catalyst. The copolymer exhibits a Mooney viscosity (ML-4/ 100 C.) of about and analyzes for the following monomer unit composition by weight; ethylene, 52; propylene, 44; 1,4-hexadiene, 4. This copolymer solution at 65 C. is deposited at the rate of 5 liters per minute on a drum dryer which is 3 feet long and 2 feet in diameter, maintained at a temperature of 145 C., and rotates at 7 revolutions per minute. The system is under a very slight vacuum. The film of copolymer left on the surface of the drum after volatilization of the solvent is stripped from the drum by contact with a standard doc-tor blade 3 feet long and 3 inches wide. The copolymer film emerging from the doctor at about C. is removed and broken up into noodles by an oscillating finger assembly operated at 30 cycles per minute. The fingers are constructed by notching a standard doctor blade (3 feet by 3 inches) to give fingers 1.5 inches long and /s-inc=h wide spaced on 4-inch centers. The entire finger assembly is lightly spring-loaded at each mounting point. Essentially the same results are obtained when the drum speed is in.- creased to 17 revolutions per minute.

Any conventional type of drum dryer can be employed in the present invention. Representative examples of these dryers are described in detail in Chemical Engineers Handbook, J. H. Perry, Third edition, McGraw-I-lill Book Co., Inc., 1950, New York, pages 863-866. Representative drum-dryers include: an atmospheric double-drum dryer, an atmospheric single-drum dryer, an atmospheric twin-drum dryer, a vacuum single dryer, and a vacuum double-drum dryer. The drum dryer can be operated, by means of suitable modifications obvious to those skilled in the art, at atmospheric pressure, subatmospheric pressure, or super-atmospheric pressure. The particularly preferred device is a double-drum dryer operated at slightly below atmospheric pressure. The temperature at which the present invention is operated is not critical and can be any value readily attainable by the equipment at hand and suitable for volatilizing the solvent under the chosen pressure.

Although the-improved drum dryer of this invention can be used to advantage in the dm-m drying of a wide variety of solutions, slurries, dispersions, and the like, it is especially useful in the drum drying of solutions or latices of polymeric materials; representative polymeric materials include polyisoprene, polybutadiene, polychloroprene, polyurethanes, polyvinyl chloride, sulfochlorinated polyethylene, styrene-butadiene copolymers, butadiene-acrylonitrile copolymers, and particularly elastomeric copolymers of ethylene and propylene such as described in US. Patents 2,933,480; 3,000,866; 3,000,867; 3,063,973; 3,093,620 and 3,093,621.

The viscosity of the solution of polymeric material employed is not critical. The viscosity limit may be selected on the basis of operating convenience in transferring solutions from the reactor and any subsequent storage stages to the surface of the drum. Where the viscosity permits, it is preferred to have as high a solids concen tration in the solution as possible. I

As previously stated, the solid polymeric material is applied to the drum in any of the manners known in the art, e.g., spraying, dip-coating, splashing, etc, either in the form of a solution or a latex.

One of the principal advantages of the invention is that it may be used to isolate solid polymeric material from a solutionor latex having relatively low solids content of polymeric material therein. Since prior art techniques depend on the formation on the drum of a self-supporting film which is subsequently taken up on a wind-up roll, they require that the concentration of polymeric material in the solution or .latex be high enough to allow a selfsupporting film .to form when the solvent is vaporized from the surface of the drum dryer. The drum dryer of this invention can thus be used in many instances Where prior art devices could not. In addition the wastage of solid polymeric material collected is greatly reduced.

What is claimed is: 1. In a drum dryer comprising a rotatable drum and a doctor knife in association with said drum for removing material deposited thereon; finger means comprising a plurality of fingers located along said doctor knife and means for oscillating said finger means along the doctoring edge of said doctor knife.

2. A drum dryer as defined in claim 1 including air knife means for directing air at said doctoring edge and finger means.

3. In a drum dryer for recovering solid polymeric material from a solution or latex thereof comprising a rotatable drum for receiving a coating of said polymeric material, and a doctor knife for removing said coating of polymeric material; finger means comprising a plate lying closely adjacent said doctor knife, said plate having a plurality of flat, equally spaced fingers projecting toward the doctoring edge of said doctor knife, and means for oscillating said finger means along said doctoring edge.

4. A drum dryer as defined in claim 3 including air knife means for directing air at said doctoring edge and finger means.

5. In a process for recovering solid polymeric material from a solution or latex thereof which comprises forming a coherent coating of said polymeric material on a rotating drum and doctoring said coating off with a doctor knife; the improvement of oscillating a plurality of fingers across said doctor knife thereby removing said solid polymeric material in particulate form.

6. A process as defined in claim 5 wherein an air stream is directed at the doctor knife at the point where the doctored coating is formed into particulate material.

FREDERICK L. MATTESON, JR., Primary NORMAN YUDKOFF, Examiner,

F. E. DRUMMOND, Assistant Examiner.

Examiner. 

5. IN A PROCESS FOR RECOVERING SOLID POLYMERIC MATERIAL FROM A SOLUTION OR LATEX THEREOF WHICH COMPRISES FORMING A COHERENT COATING OF SAID POLYMERIC MATERIAL ON A ROTATING DRUM AND DOCTORING SAID COATING OFF WITH A DOCTOR KNIFE; THE IMPROVEMENT OF OSCILLATING A PLURALITY OF FINGERS ACROSS SAID DOCTOR KNIFE THEREBY REMOVING SAID SOLID POLYMERIC MATERIAL IN PARTICULATE FORM. 